Physicochemical Properties of Cassava Starch Fermented by Indigenous-Tapai Yeasts

Tapai is a cassava food product fermented by yeast starter ("Ragi"). Among the amylolitic yeasts that had been isolated from the tapai were Candida guilliermondk C tropicalis, Trichosporon mucoides, and Saccharomycopsis fibuligera. The aim of this research was to characterize the physicochemical properties of fermented cassava starch by amylolytic yeasts of indigenus tapai i.e. C. guilliermondk C tropicalis, T mucoides, and S. fibuligera. The process of fermentation of cassava starch was done by inoculating each pure isolate by 5% v / v (10(5) CFU / ml) into cassava starch suspension 50% b/v (100g starch into 200ml sterile distilled water). The incubation was carried out at 28 degrees C for 24 h, 48 h, and 72 h. The fermented cassava starch was dried at 50 degrees C for 24 h. Characterization of physicochemical properties of cassava starch included chemical properties (amylose content), paste properties (RVA), thermal properties (DSC), physical properties (SEM granule macrostructure) and functional groups (FT-IR) of unfermented (native) or fermented cassava starch. The results showed that during the fermentation process, the yeast was able to grow up to 7 log(10) CFU/ml and the acidity decreased to pH 3,9. The amylose content of fermented cassava starch decreased to 11,22% from native starch amylose content (15,85%). The paste properties of fermented cassava starch increased at the value of trough viscosity, breakdown, final viscosity, and swelling power. The thermal properties of fermented cassava starch increased to 64,7-67 degrees C for the initial temperature value of gelatinization (To), 69,1-71,2 degrees C for gelatinization peak temperature (Tp), 73,9-75 degrees C for the final temperature of gelatinization (Tc), but decreased gelatinization enthalpy in the range of Delta H 4,84-6,38 J/g. The macrostructure of the longest fermented starch granules (72 hours)occurred liberation into irregular granular shapes. The profile of fermented cassava starch functional groups had a similarity with native cassava starch that had the highest absorption spectra at 3291,2 cm(-1) peak (vibration of the O-H bonding group) and 2920 cm(-1) peak (C-H group vibration).